1. Field of the Invention
The present invention relates to a digital broadcasting system and a method for use in the digital broadcasting system, and more specifically relates to a digital broadcasting system that transmits an event message and an event message transmission method.
2. Description of the Related Art
Efforts are recently being made to provide digital broadcasting services. In Japan, BS (broadcasting satellite) digital broadcasting services have started in December 2000 and it is planned to begin digital broadcasting services using ground waves in 2003.
Among these digital broadcasting services, there is data broadcasting where interactive contents are provided to viewers. The data broadcasting is described in detail in various documents, such as “Data Coding and Transmission Specification for Digital Broadcasting” (ARIB STD-B24, Ver. 1.0) and “Operational Guidelines for Digital Satellite Broadcasting Services Using Broadcasting Satellites” (ARIB TR-B15, Ver. 1.0)).
An event message transmission method is used in the digital broadcasting. With this method, immediately after the instruction to transmit an event message (message information) is inputted or at a specified time to transmit the event message, the event message is transmitted from a broadcast station to each receiver that runs an application. After receiving the event message, each receiver displays the event message on a television screen or performs predetermined processing (event processing) using the event message as a trigger. Note that there are two types of event messages: event messages (called “manual event messages” in this specification) that are transmitted immediately after the instructions to transmit the event messages are inputted and event messages (called “time event messages” in this specification) that are transmitted at specified times.
FIG. 1 is a block diagram showing the construction of a conventional digital broadcasting system 500. The digital broadcasting system 500 is a computer system that supports the process from the production and editing of contents for digital broadcasting to the transmission of the contents over broadcasting waves. As shown in FIG. 1, the digital broadcasting system 500 includes an authoring unit 501, a content storing unit 520, a content registering unit 530, and a transmission system 510. The transmission system 510 includes a video and audio transmission control unit 511, a content transmission control unit 512, a manual event message generating and issuing unit (hereinafter abbreviated to “manual event message unit”) 513, and a multiplexing unit 514.
The authoring unit 501 is an editing apparatus that produces contents for data broadcasts (the contents for data broadcasts are hereinafter simply referred to as the “contents”).
The content storing unit 520 is a storing apparatus that stores the produced contents. FIG. 1 shows an example content (a content 521) stored in the content storing unit 520. As shown in this drawing, the content 521 includes various files that can be roughly classified into three types of files: a content structure information file 522, scene information files 523, and monomedia information files 524.
The content structure information file 522 is a file that holds information concerning the whole structure of the content 521. Each scene information file 523 includes scene information specifying the components of a display screen. Each monomedia information file 524 includes a monomedia, such as a bitmap, that is a component of a scene.
The content registering unit 530 reads, according to a certain schedule, the contents stored in the content storing unit 520, converts the read contents to be in a MPEG2 section format, and registers the converted contents at the transmission system 510 (transfers the converted contents to the content transmission control unit 512).
The video and audio transmission control unit 511 is a real-time encoder that reads video and audio information from a VTR (videotape recorder) or another apparatus, generates MPEG2 elementary streams (video streams and audio streams) by subjecting the video and audio information to compression coding, and outputs the MPEG2 elementary streams to the multiplexing unit 514.
The content transmission control unit 512 performs the following operations according to a certain program schedule. The content transmission control unit 512 generates carousel data streams from the contents sent from the content registering unit 530 and outputs the carousel data streams to the multiplexing unit 514. Note that the carousel data streams are streams of information (carousel data) that is to be repeatedly broadcasted with a data carousel method.
The manual event message unit 513 is a terminal apparatus that includes a manual event message storing unit 513a, such as a hard disc drive apparatus, and includes a graphical user interface for an operator. According to the instructions inputted by the operator through the graphical user interface, the manual event message unit 513 generates and edits a manual event message and stores the manual event message in the manual event message storing unit 513a. Immediately after receiving an operator's instruction to issue the manual event message, the manual event message unit 513 reads the manual event message from the manual event message storing unit 513a and outputs the read manual event message to the multiplexing unit 514.
The multiplexing unit 514 generates packets from the video and audio streams, carousel data streams, and manual event message that are respectively sent from the video and audio transmission control unit 511, the content transmission control unit 512, and the manual event message unit 513. The multiplexing unit 514 then multiplexes the packets to generate a transport stream and transmits the transport stream over a broadcasting wave.
The following description concerns the processing of a manual event message 3 shown in FIG. 1 by the conventional digital broadcasting system 500 having the stated construction.
The operation procedure that should be performed by each receiver that receives the manual event message 3 is embedded into the content 521 as a program by the authoring unit 501. More specifically, as shown in FIG. 1, the operation procedure is written as a program in a scene information file 523a. In this example, the scene information file 523a includes a program for having each receiver that receives the event message 3 display message data included in the event message 3 on a screen.
The operator defines (generates) each manual event message by interacting with the manual event message unit 513 and each defined manual event message is stored in the manual event message storing unit 513a. Here, like a manual event message 513b shown in FIG. 1, each manual event message includes a name ID, a message ID, message data, the number of transmissions, and a transmission interval.
Immediately after receiving an operator's instruction to transmit a manual event message, the manual event message unit 513 repeatedly outputs a message ID and message data of the event message to the multiplexing unit 514 at a specified transmission interval for a specified number of times(corresponding to the number of transmissions included in the event message).
Each receiver has already received a program corresponding to the manual event message (a program having the message ID of the manual event message). Therefore, immediately after receiving the manual event message, each receiver displays message data included in the manual event message by superimposing the message data on a current image displayed on a television screen. As a result, urgent messages (such as the report of an earthquake) that need to be asynchronously transmitted is immediately transmitted from a broadcast station to each receiver.